NAME | SYNOPSIS | DESCRIPTION | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON

FTS(3)                    Linux Programmer's Manual                   FTS(3)

NAME         top

       fts,  fts_open, fts_read, fts_children, fts_set, fts_close - traverse
       a file hierarchy

SYNOPSIS         top

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fts.h>

       FTS *fts_open(char * const *path_argv, int options,
                     int (*compar)(const FTSENT **, const FTSENT **));

       FTSENT *fts_read(FTS *ftsp);

       FTSENT *fts_children(FTS *ftsp, int instr);

       int fts_set(FTS *ftsp, FTSENT *f, int instr);

       int fts_close(FTS *ftsp);

DESCRIPTION         top

       The fts functions are provided for traversing file hierarchies.  A
       simple overview is that the fts_open() function returns a "handle"
       (of type FTS *) that refers to a file hierarchy "stream".  This
       handle is then supplied to the other fts functions.  The function
       fts_read() returns a pointer to a structure describing one of the
       files in the file hierarchy.  The function fts_children() returns a
       pointer to a linked list of structures, each of which describes one
       of the files contained in a directory in the hierarchy.

       In general, directories are visited two distinguishable times; in
       preorder (before any of their descendants are visited) and in
       postorder (after all of their descendants have been visited).  Files
       are visited once.  It is possible to walk the hierarchy "logically"
       (visiting the files that symbolic links point to) or physically
       (visiting the symbolic links themselves), order the walk of the
       hierarchy or prune and/or revisit portions of the hierarchy.

       Two structures (and associated types) are defined in the include file
       <fts.h>.  The first type is FTS, the structure that represents the
       file hierarchy itself.  The second type is FTSENT, the structure that
       represents a file in the file hierarchy.  Normally, an FTSENT
       structure is returned for every file in the file hierarchy.  In this
       manual page, "file" and "FTSENT structure" are generally
       interchangeable.

       The FTSENT structure contains fields describing a file.  The
       structure contains at least the following fields (there are
       additional fields that should be considered private to the
       implementation):

           typedef struct _ftsent {
               unsigned short  fts_info;     /* flags for FTSENT structure */
               char           *fts_accpath;  /* access path */
               char           *fts_path;     /* root path */
               short           fts_pathlen;  /* strlen(fts_path) */
               char           *fts_name;     /* filename */
               short           fts_namelen;  /* strlen(fts_name) */
               short           fts_level;    /* depth (-1 to N) */
               int             fts_errno;    /* file errno */
               long            fts_number;   /* local numeric value */
               void           *fts_pointer;  /* local address value */
               struct _ftsent *fts_parent;   /* parent directory */
               struct _ftsent *fts_link;     /* next file structure */
               struct _ftsent *fts_cycle;    /* cycle structure */
               struct stat    *fts_statp;    /* stat(2) information */
           } FTSENT;

       These fields are defined as follows:

       fts_info    One of the following values describing the returned
                   FTSENT structure and the file it represents.  With the
                   exception of directories without errors (FTS_D), all of
                   these entries are terminal, that is, they will not be
                   revisited, nor will any of their descendants be visited.

                   FTS_D       A directory being visited in preorder.

                   FTS_DC      A directory that causes a cycle in the tree.
                               (The fts_cycle field of the FTSENT structure
                               will be filled in as well.)

                   FTS_DEFAULT Any FTSENT structure that represents a file
                               type not explicitly described by one of the
                               other fts_info values.

                   FTS_DNR     A directory which cannot be read.  This is an
                               error return, and the fts_errno field will be
                               set to indicate what caused the error.

                   FTS_DOT     A file named "."  or ".."  which was not
                               specified as a filename to fts_open() (see
                               FTS_SEEDOT).

                   FTS_DP      A directory being visited in postorder.  The
                               contents of the FTSENT structure will be
                               unchanged from when it was returned in
                               preorder, that is, with the fts_info field
                               set to FTS_D.

                   FTS_ERR     This is an error return, and the fts_errno
                               field will be set to indicate what caused the
                               error.

                   FTS_F       A regular file.

                   FTS_NS      A file for which no stat(2) information was
                               available.  The contents of the fts_statp
                               field are undefined.  This is an error
                               return, and the fts_errno field will be set
                               to indicate what caused the error.

                   FTS_NSOK    A file for which no stat(2) information was
                               requested.  The contents of the fts_statp
                               field are undefined.

                   FTS_SL      A symbolic link.

                   FTS_SLNONE  A symbolic link with a nonexistent target.
                               The contents of the fts_statp field reference
                               the file characteristic information for the
                               symbolic link itself.

       fts_accpath A path for accessing the file from the current directory.

       fts_path    The path for the file relative to the root of the
                   traversal.  This path contains the path specified to
                   fts_open() as a prefix.

       fts_pathlen The length of the string referenced by fts_path.

       fts_name    The name of the file.

       fts_namelen The length of the string referenced by fts_name.

       fts_level   The depth of the traversal, numbered from -1 to N, where
                   this file was found.  The FTSENT structure representing
                   the parent of the starting point (or root) of the
                   traversal is numbered -1, and the FTSENT structure for
                   the root itself is numbered 0.

       fts_errno   If fts_children() or fts_read() returns an FTSENT
                   structure whose fts_info field is set to FTS_DNR,
                   FTS_ERR, or FTS_NS, the fts_errno field contains the
                   error number (i.e., the errno value) specifying the cause
                   of the error.  Otherwise, the contents of the fts_errno
                   field are undefined.

       fts_number  This field is provided for the use of the application
                   program and is not modified by the fts functions.  It is
                   initialized to 0.

       fts_pointer This field is provided for the use of the application
                   program and is not modified by the fts functions.  It is
                   initialized to NULL.

       fts_parent  A pointer to the FTSENT structure referencing the file in
                   the hierarchy immediately above the current file, that
                   is, the directory of which this file is a member.  A
                   parent structure for the initial entry point is provided
                   as well, however, only the fts_level, fts_number, and
                   fts_pointer fields are guaranteed to be initialized.

       fts_link    Upon return from the fts_children() function, the
                   fts_link field points to the next structure in the NULL-
                   terminated linked list of directory members.  Otherwise,
                   the contents of the fts_link field are undefined.

       fts_cycle   If a directory causes a cycle in the hierarchy (see
                   FTS_DC), either because of a hard link between two
                   directories, or a symbolic link pointing to a directory,
                   the fts_cycle field of the structure will point to the
                   FTSENT structure in the hierarchy that references the
                   same file as the current FTSENT structure.  Otherwise,
                   the contents of the fts_cycle field are undefined.

       fts_statp   A pointer to stat(2) information for the file.

       A single buffer is used for all of the paths of all of the files in
       the file hierarchy.  Therefore, the fts_path and fts_accpath fields
       are guaranteed to be null-terminated only for the file most recently
       returned by fts_read().  To use these fields to reference any files
       represented by other FTSENT structures will require that the path
       buffer be modified using the information contained in that FTSENT
       structure's fts_pathlen field.  Any such modifications should be
       undone before further calls to fts_read() are attempted.  The
       fts_name field is always null-terminated.

   fts_open()
       The fts_open() function takes a pointer to an array of character
       pointers naming one or more paths which make up a logical file
       hierarchy to be traversed.  The array must be terminated by a null
       pointer.

       There are a number of options, at least one of which (either
       FTS_LOGICAL or FTS_PHYSICAL) must be specified.  The options are
       selected by ORing the following values:

       FTS_COMFOLLOW This option causes any symbolic link specified as a
                     root path to be followed immediately whether or not
                     FTS_LOGICAL is also specified.

       FTS_LOGICAL   This option causes the fts routines to return FTSENT
                     structures for the targets of symbolic links instead of
                     the symbolic links themselves.  If this option is set,
                     the only symbolic links for which FTSENT structures are
                     returned to the application are those referencing
                     nonexistent files.  Either FTS_LOGICAL or FTS_PHYSICAL
                     must be provided to the fts_open() function.

       FTS_NOCHDIR   As a performance optimization, the fts functions change
                     directories as they walk the file hierarchy.  This has
                     the side-effect that an application cannot rely on
                     being in any particular directory during the traversal.
                     The FTS_NOCHDIR option turns off this optimization, and
                     the fts functions will not change the current
                     directory.  Note that applications should not
                     themselves change their current directory and try to
                     access files unless FTS_NOCHDIR is specified and
                     absolute pathnames were provided as arguments to
                     fts_open().

       FTS_NOSTAT    By default, returned FTSENT structures reference file
                     characteristic information (the statp field) for each
                     file visited.  This option relaxes that requirement as
                     a performance optimization, allowing the fts functions
                     to set the fts_info field to FTS_NSOK and leave the
                     contents of the statp field undefined.

       FTS_PHYSICAL  This option causes the fts routines to return FTSENT
                     structures for symbolic links themselves instead of the
                     target files they point to.  If this option is set,
                     FTSENT structures for all symbolic links in the
                     hierarchy are returned to the application.  Either
                     FTS_LOGICAL or FTS_PHYSICAL must be provided to the
                     fts_open() function.

       FTS_SEEDOT    By default, unless they are specified as path arguments
                     to fts_open(), any files named "."  or ".."
                     encountered in the file hierarchy are ignored.  This
                     option causes the fts routines to return FTSENT
                     structures for them.

       FTS_XDEV      This option prevents fts from descending into
                     directories that have a different device number than
                     the file from which the descent began.

       The argument compar() specifies a user-defined function which may be
       used to order the traversal of the hierarchy.  It takes two pointers
       to pointers to FTSENT structures as arguments and should return a
       negative value, zero, or a positive value to indicate if the file
       referenced by its first argument comes before, in any order with
       respect to, or after, the file referenced by its second argument.
       The fts_accpath, fts_path, and fts_pathlen fields of the FTSENT
       structures may never be used in this comparison.  If the fts_info
       field is set to FTS_NS or FTS_NSOK, the fts_statp field may not
       either.  If the compar() argument is NULL, the directory traversal
       order is in the order listed in path_argv for the root paths, and in
       the order listed in the directory for everything else.

   fts_read()
       The fts_read() function returns a pointer to an FTSENT structure
       describing a file in the hierarchy.  Directories (that are readable
       and do not cause cycles) are visited at least twice, once in preorder
       and once in postorder.  All other files are visited at least once.
       (Hard links between directories that do not cause cycles or symbolic
       links to symbolic links may cause files to be visited more than once,
       or directories more than twice.)

       If all the members of the hierarchy have been returned, fts_read()
       returns NULL and sets the external variable errno to 0.  If an error
       unrelated to a file in the hierarchy occurs, fts_read() returns NULL
       and sets errno appropriately.  If an error related to a returned file
       occurs, a pointer to an FTSENT structure is returned, and errno may
       or may not have been set (see fts_info).

       The FTSENT structures returned by fts_read() may be overwritten after
       a call to fts_close() on the same file hierarchy stream, or, after a
       call to fts_read() on the same file hierarchy stream unless they
       represent a file of type directory, in which case they will not be
       overwritten until after a call to fts_read() after the FTSENT
       structure has been returned by the function fts_read() in postorder.

   fts_children()
       The fts_children() function returns a pointer to an FTSENT structure
       describing the first entry in a NULL-terminated linked list of the
       files in the directory represented by the FTSENT structure most
       recently returned by fts_read().  The list is linked through the
       fts_link field of the FTSENT structure, and is ordered by the user-
       specified comparison function, if any.  Repeated calls to
       fts_children() will re-create this linked list.

       As a special case, if fts_read() has not yet been called for a
       hierarchy, fts_children() will return a pointer to the files in the
       logical directory specified to fts_open(), that is, the arguments
       specified to fts_open().  Otherwise, if the FTSENT structure most
       recently returned by fts_read() is not a directory being visited in
       preorder, or the directory does not contain any files, fts_children()
       returns NULL and sets errno to zero.  If an error occurs,
       fts_children() returns NULL and sets errno appropriately.

       The FTSENT structures returned by fts_children() may be overwritten
       after a call to fts_children(), fts_close(), or fts_read() on the
       same file hierarchy stream.

       The instr argument is either zero or the following value:

       FTS_NAMEONLY Only the names of the files are needed.  The contents of
                    all the fields in the returned linked list of structures
                    are undefined with the exception of the fts_name and
                    fts_namelen fields.

   fts_set()
       The function fts_set() allows the user application to determine
       further processing for the file f of the stream ftsp.  The fts_set()
       function returns 0 on success, and -1 if an error occurs.

       The instr argument is either 0 (meaning "do nothing") or one of the
       following values:

       FTS_AGAIN    Revisit the file; any file type may be revisited.  The
                    next call to fts_read() will return the referenced file.
                    The fts_stat and fts_info fields of the structure will
                    be reinitialized at that time, but no other fields will
                    have been changed.  This option is meaningful only for
                    the most recently returned file from fts_read().  Normal
                    use is for postorder directory visits, where it causes
                    the directory to be revisited (in both preorder and
                    postorder) as well as all of its descendants.

       FTS_FOLLOW   The referenced file must be a symbolic link.  If the
                    referenced file is the one most recently returned by
                    fts_read(), the next call to fts_read() returns the file
                    with the fts_info and fts_statp fields reinitialized to
                    reflect the target of the symbolic link instead of the
                    symbolic link itself.  If the file is one of those most
                    recently returned by fts_children(), the fts_info and
                    fts_statp fields of the structure, when returned by
                    fts_read(), will reflect the target of the symbolic link
                    instead of the symbolic link itself.  In either case, if
                    the target of the symbolic link does not exist, the
                    fields of the returned structure will be unchanged and
                    the fts_info field will be set to FTS_SLNONE.

                    If the target of the link is a directory, the preorder
                    return, followed by the return of all of its
                    descendants, followed by a postorder return, is done.

       FTS_SKIP     No descendants of this file are visited.  The file may
                    be one of those most recently returned by either
                    fts_children() or fts_read().

   fts_close()
       The fts_close() function closes the file hierarchy stream referred to
       by ftsp and restores the current directory to the directory from
       which fts_open() was called to open ftsp.  The fts_close() function
       returns 0 on success, and -1 if an error occurs.

ERRORS         top

       The function fts_open() may fail and set errno for any of the errors
       specified for open(2) and malloc(3).

       The function fts_close() may fail and set errno for any of the errors
       specified for chdir(2) and close(2).

       The functions fts_read() and fts_children() may fail and set errno
       for any of the errors specified for chdir(2), malloc(3), opendir(3),
       readdir(3), and stat(2).

       In addition, fts_children(), fts_open(), and fts_set() may fail and
       set errno as follows:

       EINVAL options or instr was invalid.

VERSIONS         top

       These functions are available in Linux since glibc2.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────────────────────────────┬───────────────┬───────────┐
       │Interface                          Attribute     Value     │
       ├───────────────────────────────────┼───────────────┼───────────┤
       │fts_open(), fts_set(), fts_close() │ Thread safety │ MT-Safe   │
       ├───────────────────────────────────┼───────────────┼───────────┤
       │fts_read(), fts_children()         │ Thread safety │ MT-Unsafe │
       └───────────────────────────────────┴───────────────┴───────────┘

CONFORMING TO         top

       4.4BSD.

BUGS         top

       In versions of glibc before 2.23, all of the APIs described in this
       man page are not safe when compiling a program using the LFS APIs
       (e.g., when compiling with -D_FILE_OFFSET_BITS=64).

SEE ALSO         top

       find(1), chdir(2), stat(2), ftw(3), qsort(3)

COLOPHON         top

       This page is part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                            2017-03-13                           FTS(3)

Pages that refer to this page: ftw(3)